1. Field of the Invention
The present invention relates to an image forming apparatus adapted to control the image forming conditions thereof based on the detected density of a toner image as a patch image, a control method for the same and an image forming method.
2. Description of the Related Art
Electrophotographic image forming apparatuses such as printers, copiers and facsimiles adopt the following method to ensure that a predetermined level of image quality is achieved in a consistent manner. Specifically, a small test image (patch image) having a predetermined image pattern is formed as required, while an image density of the image is detected by means of a density sensor. Then, operating conditions of individual parts of the apparatus are controlled based on the detection result.
In an image forming apparatus disclosed in Japanese Patent Application Laid-Open Gazette No. 2000-333012, for example, tone correction characteristics of the apparatus are controlled based on the detected density of the patch image. Specifically, the apparatus detects a density of the test image of the predetermined pattern by means of a patch sensor. Gamma characteristics of the apparatus are grasped from the detection results so as to generate a corrective conversion table for tone correction. Referring to the new corrective conversion table thus generated, the apparatus converts an image signal into data indicative of a laser pulse width. As a result, there may be obtained an optimum print result corresponding to the variations of the gamma characteristics of the apparatus.
According to the common tone correction technique of this type, the patch images are formed only at some typical tone levels. The gamma characteristics of the apparatus are estimated from the detected densities of such path images so as to determine the tone correction characteristics of the apparatus. More recently, however, there is an increasing demand for higher image quality, which dictates the need to establish a tone correction technique providing a more exact and more accurate tone correction.